Published: May 2003
Prescriber Update 24(1): 12
Medsafe Editorial Team
Prescribers are reminded of the potentially severe interaction between miconazole oral gel (Daktarin® oral gel) and warfarin. Clinically significant increases in the international normalised ratio (INR) of patients who have been stabilised on warfarin can occur following concomitant use of miconazole oral gel.
Significant systemic absorption of miconazole oral gel can occur when the oral mucosa is inflamed, or from the bowel after the gel has been swallowed. The interaction with warfarin is probably less likely when miconazole is administered to the skin or vaginally but in Australia there has been one report of an interaction involving topical miconazole cream.1
In other reports in Australia, the increase in INR has usually occurred within a week or two of commencing miconazole oral gel. In the 17 patients on warfarin in whom INR values were known, the INR rose to between 7.5 and more than 18. In eight of these cases, patients presented with bruising, haematuria or mucocutaneous bleeding. Most patients required the withdrawal of one or both medicines.1
There have been six reports in New Zealand of the warfarin and miconazole oral gel interaction resulting in INR increases. Four patients presented with bleeding symptoms such as haemarthrosis, haematuria, haemoptysis or epistaxis. INR values ranged from 7.5 to 18 and those patients with bleeding symptoms all had an INR in excess of 10.
As miconazole oral gel can be purchased from pharmacists, without a prescription, both pharmacists and prescribers are reminded to inform patients taking warfarin about the potential for miconazole oral gel to interact with warfarin. Patients taking warfarin who are also given miconazole oral gel should be monitored for change in anticoagulant effect and the dose of warfarin adjusted, if necessary.2 Both the data sheet and Consumer Medicine Information (CMI) for Daktarin oral gel contain warnings about this interaction.
Competing interests (authors): none declared.